1. Field of the Invention
The present invention relates to a rotational injection molding machine which is able to mold at least a pair of half hollow products and a hollow product consisted of a pair of half hollow products combined in an abutted state successively.
2. Description of the Prior Art
Conventionally, there has been proposed an injection molding machine for molding plastic hollow products (See, for instance, Japanese Patent Laid-open publication No. Sho 62-87315). This molding machine has a pair of molds one of which is slidable relative to the other wherein each mold has a pair of male and female dies arranged in a length-wise direction thereof but in an order of arrangement with each other.
In operation, individual half hollow products are molded by positioning the slidable mold at a first position. Next, after opening the pair of molds, the slidable mold is moved to a second position so that the half hollow products thus molded abut each other when the other mold is clamped to the slidable mold. In this state, a secondary molding is produced by supplying molten resin around the butted ends of the half hollow products to connect or merge them with each other.
This molding machine is advantageous in that the primary and secondary injection moldings can be made successively only by sliding the slidable mold.
However, in this molding machine, the injection amount at the secondary injection molding is quite small in comparison with that at the primary injection molding and it becomes necessary to adjust the injection amount at every injection molding so that it is quite difficult to control the injection amount.
Further, since both male dies are maintained in an idle state upon the secondary injection molding in which only female dies are used, the temperature of each male die lowers during the second injection molding process while each female die is maintained at a relatively high temperature. This makes it necessary to compensate for the temperature drop of the male die.